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The Impact of a Rectal Hydrogel Spacer on Dosimetric and Toxicity Outcomes Among Patients Undergoing Combination Therapy with External Beam Radiotherapy and Low-Dose-Rate Brachytherapy - Beyond the Abstract

In recent years, numerous efforts have been made to shorten treatment courses and reduce gastrointestinal and genitourinary toxicity in patients who receive radiation therapy for prostate cancer. Among these advances is the rise of stereotactic body radiation therapy (SBRT), which allows for the delivery of full treatment courses over fewer fractions than conventional radiation therapy techniques. Prior research has indicated that this approach has largely been successful, as patients treated with SBRT experience high rates of disease control and low rates of toxicity.1-4 In addition, the use of rectal hydrogel spacers, which increase the distance between the prostate and rectum in an attempt to reduce treatment toxicity, is becoming more widespread. Prior studies have demonstrated reductions in radiation dose exposure to the rectum in patients with rectal hydrogel spacers who are treated with external beam radiation therapy (EBRT), along with fewer gastrointestinal and genitourinary toxicities and improvements in reported quality of life.5, 6


Rectal hydrogel spacers may also be utilized in patients receiving low-dose-rate (LDR) brachytherapy. Prior work by Tagger et al., which evaluated the effects of rectal hydrogel spacers placed after Palladium-103 LDR implantation but before the receipt of external beam radiation therapy, found that patients received sufficient prescription dose coverage of the prostate and low rectal dose exposure.7 At our institution, the treatment sequence differs. In fact, we place the rectal hydrogel spacer prior to external beam radiation therapy, which is then followed by LDR brachytherapy. Data on the impact of rectal hydrogel spacers in this setting is limited. Thus, in this study, we sought to compare prostate and rectal dosimetric outcomes, as well as acute toxicities, among patients undergoing EBRT and LDR brachytherapy at our institution who had and had not received rectal hydrogel spacers.

We identified all patients with intermediate- and high-risk prostate cancer who were treated definitively with combination therapy (EBRT + LDR brachytherapy ± androgen deprivation therapy (ADT)) at our institution between 2014 and 2019. EBRT was delivered via either SBRT (25 Gray (Gy) in 5 fractions) or conventional fractionation (45 Gy in 25 fractions). LDR brachytherapy was delivered via the placement of Palladium-103 seeds into the prostate 1-3 weeks after the completion of EBRT to a prescription dose of 100 Gy. Dosimetric outcomes were calculated using the one-month post-implant dosimetry scan.

168 patients met our inclusion criteria. 22 of these patients (13.1%) underwent rectal hydrogel spacer placement prior to EBRT, while 146 (86.9%) patients did not. The groups were well balanced for age, Gleason score, National Comprehensive Cancer Network risk grouping, prostate volume, prostate-specific antigen, race, T stage, and usage of ADT. Additionally, there were no differences in baseline International Prostate Symptom Score (I-PSS) and Sexual Health Inventory for Men (SHIM) scores between the groups.

Among patients who received a rectal hydrogel spacer, the mean separation between the prostate and rectum was 7.5 millimeters and the volume of the rectum that received at least 100 Gy was 47% lower than in patients who did not receive a rectal hydrogel spacer. However, there were no differences between the two groups in the mean rates of change in I-PSS and SHIM scores at two and twelve months after the completion of their post-implant dosimetry scans. At the same time, there were no statistically significant differences among the two groups in terms of the proportion of patients who received a dose of at least 100 Gy to 90% of the prostate or in the median percentage of the volume of prostate that received at least 100 Gy and 150 Gy.

We believe that this is the first study to examine dosimetric and quality-of-life outcomes in patients who receive rectal hydrogel spacers prior to both EBRT and LDR brachytherapy. While there are a number of limitations to this study, including (and not limited to) its retrospective nature and small sample size, our results suggest that it is in fact possible to achieve a high-quality LDR implant that does not sacrifice prescription dose coverage of the prostate after rectal hydrogel spacer placement. Additionally, rectal hydrogel spacers appear to increase the distance between the prostate and rectum and result in reduced radiation dose exposure to the rectum. While we did not find any differences in quality of life scores between the two groups, the length of follow-up was limited in the rectal hydrogel spacer group. Future studies will be necessary to confirm these findings.

Written by: Anthony D. Nehlsen, Kunal K. Sindhu, Erin Moshier, John P. Sfakianos, Richard G. Stock, Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai, New York, New York

References:

  1. Van As NJ, Brand D, Tree A, et al. PACE: analysis of acute toxicity in PACE-B, an international phase Ill randomized controlled trial comparing stereotactic body radiotherapy (SBRT) to conventionally fractionated or moderately hypofractionated external beam radiotherapy (CFMHRT) for localized prostate cancer (LPCa). J Clin Oncol 2019;37(7).
  2. Lukka HR, Pugh SL, Bruner DW, et al. Patient reported outcomes in NRG oncology RTOG 0938, evaluating two ultrahypofractionated regimens for prostate cancer. Int J Radiat Oncol Biol Phys 2018; 102:287e295.
  3. Meier RM, Bloch DA, Cotrutz C, et al. Multicenter trial of stereotactic body radiation therapy for low- and intermediate-risk prostate cancer: survival and toxicity endpoints. Int J Radiat Oncol Biol Phys 2018;102:296e303.
  4. Kishan AU, Dang A, Katz AJ, et al. Long-term outcomes of stereotactic body radiotherapy for low-risk and intermediate-risk prostate cancer. JAMA Netw Open 2019;2(2):e188006.
  5. Wu SY, Boreta L, Wu A, et al. Improved rectal dosimetry with the use of SpaceOAR during high-dose-rate brachytherapy. Brachytherapy 2018;17:259e264.
  6. Hamstra DA, Boreta L, Wu A, et al. Continued benefit to rectal separation for prostate radiation therapy: final results of a phase III trial. Int J Radiat Oncol Biol Phys 2017;97:976e985.
  7. Taggar AS, Charas T, Cohen GN, et al. Placement of an absorbable rectal hydrogel spacer in patients undergoing low-dose-rate brachytherapy with palladium-103. Brachytherapy 2018;17:251e258.
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